Yup. Ive seen fully built engines produce 500hp when their purpose was 700hp. Threw a ton of money at it trying to figure it out. Finally, by shear luck, noticed valves not seating, after 3 tare downs(we learned alot from that truck)not noticing the valve situation...lashers were the problem. We shimmed check the valve to seat opening and it was .020" ....every valve.
Why did it run? ....normal operations will force the valves closed, but at the wrong time.
Swapped out the lashers, dyno'd 700rwhp.
Since every part was new, we came to the conclusion it was his break in oil used. It was specific high dollar break in oil from a big reputable name i will not disclose. And since my buddy buys nothing but the best due to his disposable cash flow, break in oil was the culprit.
Now dont think the use of break in oil are the only reason lashers goof up. Overdue oil changes, high milage, and heavier oil weights also cause this.
Just some ideas to crunch on. I want you to be as successful as you can be with your build.